CN102553450B - A Method for Preventing Separation MBR Flat Membrane Fouling - Google Patents

Abstract

The invention discloses a method for preventing fouling of split-type MBR flat membranes, which includes adding bottom and top screens to a membrane module box, adding granular fillers between the screens, and the diameter of the granular fillers is larger than the mesh diameter of the screens. In the method of the invention, filler particles are added to the membrane bioreactor to circulate and stir in the membrane module, which makes up for the lack of shear force on the membrane surface caused by ordinary aeration, and improves the cleaning effect on the membrane surface. Under the premise of not increasing the aeration rate much, not damaging the membrane surface, and not affecting the effluent water quality, the risk of membrane fouling is reduced, the frequency of chemical cleaning is effectively reduced, and the interval between membrane cleaning is extended by about 30%. It is a low-cost, high-efficiency method for preventing and controlling membrane fouling.

Description

A Method for Preventing Separation MBR Flat Membrane Fouling

technical field

The invention relates to a method for preventing fouling of a split-type MBR flat membrane and a split-type membrane bioreactor capable of controlling the fouling of the membrane.

Background technique

The Membrane Bio-Reactor (MBR) process is a water treatment technology that combines high-efficiency membrane separation technology with activated sludge biological treatment units. Its biggest feature is that it combines the two widely used physical and chemical treatment and biological treatment methods in water treatment.

The removal of pollutants by the MBR process is based on the biochemical mechanism of activated sludge and the physical and chemical mechanism of membrane filtration. The metabolism of activated sludge is the central link in the removal of pollutants, and there is a synergy between biochemical degradation and membrane separation. The activated sludge process is currently the most widely used secondary biological treatment technology in the world, and the introduction of membrane separation technology into the activated sludge process has substantially changed the mud-water separation technology of the activated sludge process, overcoming the traditional method. The disadvantages of sludge loss and swelling are completely separated from the hydraulic retention time (HRT) and sludge retention time (SRT), which is conducive to the growth of slow-growing microorganisms such as refractory organic matter decomposing bacteria.

Compared with traditional biological treatment processes, MBR has the advantages of simple process, high efficiency, high sludge concentration, low residual sludge output, good effluent quality, small equipment footprint, and strong impact load resistance. The effluent water quality can reach or be better than the "People's Republic of China Miscellaneous Domestic Water Quality Standard (GJ25.1-89)", and can be directly used as water for reclaimed water reuse, urban landscaping, sweeping, fire protection, etc. Moreover, the interception effect of the membrane enables the slow-growing microbial strains to reproduce and grow, expanding the application range of the MBR process. This technology is a sewage treatment technology that has developed rapidly in recent years and has become one of the current research and application hotspots.

According to the different ways of combining membrane modules and bioreactors, there are currently two main MBR process configurations: submerged and split. The hydraulic operation mode also includes two types: pump lift type and air lift type. In addition, there are two other membrane process modes, namely extraction and diffusion, but the role of the membrane in these two modes is not to separate microorganisms from water. In terms of membrane elements, although there are membrane products with different geometries and configurations in the membrane market, there are three types that dominate commercial MBR technologies, namely flat-sheet membranes, hollow fibers and multi-tube membranes.

The submerged MBR is to directly immerse the membrane module in the activated sludge reaction for separation, without the mixed liquid loop of the external membrane bioreactor. The leachate is driven by negative pressure suction or gravity head, and is separated and discharged through the membrane surface. Aeration is usually carried out under the membrane module. The upward movement of the bubbles can trigger the internal circulation of the liquid, generate sufficient gas-liquid mixing shear force, and wash the membrane surface, thereby reducing the deposition of sludge on the membrane surface. To a certain extent It can achieve the purpose of controlling and slowing down membrane fouling.

In a split MBR, the membrane modules are independent of the bioreactor. The mud-water mixture is sent to the membrane module unit in the loop by the circulating pump. Driven by the pressure difference, the leachate is separated by membrane filtration and discharged, and the retained mixed solution is returned to the reaction tank. The split MBR operates through the cross-flow of material-liquid circulation, and its characteristics are: stable and reliable operation, easy operation and management, and easy replacement and addition of membrane modules. The transmembrane pressure (Transmembrane Pressure, TMP) and cross-flow rate of the split MBR are both generated by the pump. Usually, in order to reduce the deposition of pollutants on the membrane surface, the circulating pump is required to provide a large flow rate of the material and liquid, so the power consumption of this type of MBR Larger, and the shear force formed by frequent and high-speed sludge backflow will destroy the sludge flocs and affect the growth and activity of microorganisms.

The main forms of membrane modules are flat plate, tubular, hollow fiber, spiral, capillary and so on. In the separated type, the flat type and the tube type are mostly used. In the integrated type, the hollow fiber type and the flat type are mostly used.

As a new process, the MBR process has been studied more in the past two years, among which there are more studies on water reuse in municipal sewage. There are already examples of MBR projects and good results have been achieved. The advantages of MBR technology, such as high sludge concentration and long sludge age, determine that it can effectively treat sewage that is difficult to treat by conventional methods. In addition to being widely used in municipal sewage reuse, this process It has also been successfully applied in high-concentration and difficult-to-treat wastewater such as landfill leachate and pharmaceutical wastewater.

Membrane bioreactor is an efficient water treatment technology, but as a new technology, it still has its own defects. Because the membrane is easily polluted during operation, the flux of the membrane decreases, and the frequency of membrane cleaning and membrane replacement increases, which directly affects the efficiency and service life of the membrane module and hinders its wide application in practice.

Membrane fouling refers to the phenomenon that certain components in the liquid to be filtered are deposited on the surface of the membrane or in the pores of the membrane, resulting in a decrease in membrane permeation, including the adsorption of small molecular solutes in the membrane pores, and the increase in membrane filtration resistance caused by the blockage of the membrane pores by macromolecular solutes. , A filter cake layer is formed on the surface of the membrane to increase the mass transfer resistance. After the membrane is fouled, its permeation flux decreases severely, the pressure across the membrane increases, and the retention efficiency decreases.

The factors affecting membrane fouling are complex, and the membrane fouling factors mainly come from three aspects: membrane properties, operating conditions and properties of activated sludge mixture. During the operation of the project, the impact of membrane fouling on the system is mainly reduced by controlling the operating conditions.

Membrane fouling control programs at this stage can be summarized into the following categories:

The aeration control scheme is mainly to remove the pollutants on the membrane surface by controlling the aeration method and intensity to form a shear force. For example, a method and device for a jet air-lift separate membrane bioreactor (application number/patent number: 200810110776), which uses the violent agitation generated by jet aeration to increase the mass transfer rate in the mixed liquid and accelerate biochemical reactions , to reduce membrane fouling. Its limitation is that the change of the aeration method will require relatively large energy consumption, and the relative energy consumption corresponding to the shear force may be greater than the energy consumption required for flushing with other media.

The external electric field or ultrasonic anti-pollution scheme mainly produces the rejection and elution of membrane pollutants through external energy. For example, a method of using a weak electric field to improve the anti-pollution performance and flux of the membrane (application number/patent number: 201010259595), which is characterized by using the principle of homosexual repulsion, applying a weak negative electric field near the membrane surface to increase the resistance to these pollutants The repulsion effect pushes the membrane pollutants away from the membrane surface, so it has the effect of delaying the formation of filter cake layer, increasing the anti-pollution performance of the membrane, increasing the flux and prolonging the filtration operation cycle. Or a method of online control of membrane fouling development by using ultrasound (application number/patent number: 200510011799). Using ultrasonic waves can effectively control the development of membrane fouling online at a relatively low cross-flow velocity on the membrane surface. This type of method mainly relies on external energy for anti-pollution, which requires additional equipment and energy consumption, and increases the difficulty of operation and daily operation and maintenance.

Anti-pollution schemes such as dosing chemicals mainly add coagulants to precipitate activated sludge or rely on the synergistic effect of zeolite powder and sludge to reduce pollution on the surface of flat membranes. For example: the integrated method and device of enhanced coagulation-airlift-membrane to reduce membrane pollution (application number/patent number: 201010101535), and coagulation of activated sludge to prevent membrane pollutants produced by sludge agglomeration. Or a method for reducing membrane pollution of flat membrane-membrane bioreactor (application number/patent number: 200410052943), adding a certain amount of zeolite powder, and relying on the synergistic effect of zeolite powder and sludge to reduce pollution on the surface of the flat membrane , effectively slowing down the decline rate of membrane flux. Dosing chemicals will increase operating costs, and adding coagulation and flocculation may affect the properties of activated sludge. The flocculant itself is a polymer compound, which may aggravate membrane fouling. Adding zeolite may only enhance the effect of denitrification, but the removal efficiency of membrane pollutants is not high, and it cannot be recovered, so the economy is poor.

The main cause of membrane fouling is the decrease in flux caused by the adsorption of high-molecular organic matter produced by microorganisms on the membrane surface. The existing membrane fouling control technology is used to reduce membrane fouling mainly to prevent the accumulation of such organic pollution on the membrane surface. This kind of high molecular organic matter is difficult to biodegrade during the treatment process. Therefore, it is necessary to enrich and transfer these pollutants to fundamentally reduce membrane fouling. Due to the strong adsorption capacity of these high-molecular organic matter, the shear force formed by aeration is not enough to remove the surface adsorbates, and the addition of energy or chemicals will increase the cost of per ton of water treatment and may affect the sludge properties.

Contents of the invention

An object of the present invention is to provide a method for preventing fouling of a separate MBR flat membrane.

Another object of the present invention is to provide a separate membrane bioreactor that can reduce membrane fouling.

The technical scheme adopted in the present invention is:

A method for preventing fouling of a separate MBR flat membrane, comprising adding bottom and top screens to the membrane module box, adding granular packing between the screens, and the diameter of the granular packing is larger than the mesh diameter of the screen.

Preferably, the particle filler is circular, which can reduce the occurrence of gap clogging.

Preferably, the particle filler has a density of 1.1-1.2 kg/m ³ .

Preferably, the volume of the granular filler is 10% to 20% of the volume of the box between the upper and lower screens.

Preferably, the granular filler is at least one of ceramsite, fruit shell, polyurethane and polypropylene.

Preferably, the particle filler has a diameter of 2-4 mm.

Preferably, the mesh diameter of the sieve is 0.5-2 mm, and further preferably, the mesh diameter is 1-2 mm, so as to ensure that the generated air bubble shear force can push the packing layer.

Preferably, a filler replacement port is provided on the membrane module box.

A separate membrane bioreactor, including a biochemical tank and a membrane tank, the membrane module box is placed in the membrane tank, the bottom and the top of the membrane module box are each equipped with a layer of screen 1, and the box between the two layers of screen is placed There is a flat membrane group 2, and a granular filler 3 is added to the box between two layers of screens, and the diameter of the granular filler is larger than the mesh diameter of the screen.

Preferably, the gap between the flat membranes in the flat membrane group of the split-type membrane bioreactor is 20-30mm, and when the air bubbles stir, the gap ratio of 6-8 times is not easy to cause blockage.

The beneficial effects of the present invention are:

(1) In the method of the present invention, filler particles are added to the membrane bioreactor to circulate and stir in the membrane module, which makes up for the lack of shear force on the membrane surface caused by ordinary aeration, and improves the cleaning effect on the membrane surface. Under the premise of not increasing the aeration rate much, not damaging the membrane surface, and not affecting the effluent water quality, the risk of membrane fouling is reduced, the frequency of chemical cleaning is effectively reduced, and the interval between membrane cleaning is extended by about 30%. It is a low-cost, high-efficiency method for preventing and controlling membrane fouling.

(2) The cost of the particles used is low, and the presence of a rigid medium can strengthen the shear force of soda on the membrane surface, and can adsorb colloids, proteins, and lipids that form pollution. The filler is cheap and can be replaced or taken out for cleaning and air-dried for continued use.

Description of drawings

Fig. 1 is a schematic structural view of a separate membrane bioreactor of the present invention;

Fig. 2 is a schematic structural view of the membrane module box of the present invention;

Fig. 3 is the MBR system of the embodiment of the present invention 1 and contrast system under the same operation condition and compares the pressure difference between the membranes;

Fig. 4 is the comparison between the MBR system of Example 1 of the present invention and the control system at the chemical cleaning time point and the corresponding membrane flux recovery rate under the same operating conditions;

Fig. 5 is the effect that adopts membrane bioreactor of the present invention to process actual printing and dyeing wastewater;

Fig. 6 is a comparison of the pressure difference between the membranes of the MBR system of Example 2 of the present invention and the control system under the same operating conditions.

Detailed ways

The present invention will be further described below in conjunction with the examples, but not limited thereto.

Embodiment 1 prevents the method 1 of separating type MBR flat membrane fouling

A split-type membrane bioreactor consists of two parts: a biochemical pool and a membrane pool, and the membrane module box is placed in the membrane pool (see Figure 1). As shown in Figure 2, the present invention sets a layer of screens 1 on the bottom and top of the membrane module box respectively, and a flat membrane group 2 is placed in the box between the two layers of screens, and the box between the two layers of screens is added Granular filler 3, the diameter of the granular filler is larger than the mesh diameter of the screen, the aeration pipe 4 is placed under the bottom screen, and the membrane module box is provided with a filler replacement window 5, which is used for filler replacement and screen cleaning.

In this example, the mesh diameter of the screen is 2mm; the particle filler used is round ceramsite, the density is 1.1kg/m ³ , the diameter is 2.5~3mm, and the total volume of the filler is the box between the upper and lower screens. 12.5% of the volume; the flat membrane group used, the gap between each flat membrane is 25mm, when the air bubbles stir, the gap ratio is not easy to cause blockage. The bottom aeration adopts high-pressure aeration, which reduces the intake air volume and increases the intake air pressure. Increase the circulation and agitation of the aeration to the filler.

Effect experiment

In the following experiments, the device of embodiment 1 of the present invention is compared with the control system, and the control system is that the device of embodiment 1 has no upper and lower screens and does not add granular fillers.

1. Membrane bioreactor of the present invention is to the inter-membrane pressure difference under the condition of permeation flow

It can be seen from Figure 3 that under the same permeation flow rate, the pressure difference between the membranes of the filler particle system can effectively reduce the time of membrane fouling under the same operating conditions. The pressure difference between the membranes of the control system was as high as 69 kpa after 200 days of operation, while the pressure difference between the membranes of the system with granular filler was 34 kpa, which effectively reduced the degree of membrane fouling. The system of adding particles can reduce the frequency of membrane cleaning, and under the same operating conditions, the running cleaning interval can be extended by 30%.

2. Chemical cleaning frequency and recovery rate

According to the comparison of the cleaning frequency and the membrane flux recovery rate after cleaning between the membrane bioreactor of the present invention and the control system in stable operation for 600 days. With the addition of particle packing, the cleaning time interval is extended, and the membrane flux recovery rate can be increased by 3-5% (see Figure 4).

3. Membrane bioreactor of the present invention is to COD removal efficiency and MLSS load

Using the membrane bioreactor of the present invention to build a system with a water production rate of 30m3/d, the COD removal rate and MLSS load are shown in Figure 5. The pilot system has been running stably for 6 months, and the effluent has been stable for 180 days. When the average sludge volume load is 8kgCOD/m3.d, the average COD removal rate is above 95%. This shows that the particle system will not have a negative impact on the membrane, while ensuring water efficiency and pollutant removal capacity.

Embodiment 2 prevents the method 2 of split-type MBR flat membrane fouling

In this example, for the separate membrane bioreactor, the mesh diameter of the screen is 1.5mm; the particle filler used is round fruit shell filler (mainly hickory shell), and the density range is 1.1~1.25 kg/m ³ , the average density is 1.15 kg/m ³ , the diameter is 1.8~3mm, and the average diameter is 2.2mm. The total volume of the filler is 20% of the volume of the box between the upper and lower screens; the flat membrane group used, the gap between each flat membrane is 20mm. The bottom aeration adopts high-pressure aeration, which reduces the intake air volume and increases the intake air pressure. Increase the circulation and agitation of the aeration to the filler.

The pressure difference between the membranes under the condition of the same permeate flow in the membrane bioreactor

It can be seen from Figure 6 that under the same permeation flow rate, the pressure difference between the membranes of the filler particle system can effectively reduce the time of membrane fouling under the same operating conditions. The system has been running for 700 days, and the pressure difference between the membranes of the system added with granular fillers has a lower rate of increase than that of the control system, which effectively reduces the degree of membrane fouling. The system with added particles can reduce the frequency of membrane cleaning, and under the same operating conditions, the running cleaning time interval can be extended.

The above embodiments are only preferred cases for introducing the present invention. For those skilled in the art, any obvious changes and improvements made within the scope of not departing from the spirit of the present invention should be regarded as a part of the present invention.

Claims (1)

1. A separate membrane bioreactor, which consists of two parts: a biochemical tank and a membrane tank. The membrane module box is placed in the membrane tank, and a layer of screen (1) is installed on the bottom and top of the membrane module box, and two layers of screen A flat membrane group (2) is placed in the box between the two layers of screens, and granular fillers (3) are added to the box between the two layers of screens. The diameter of the granular fillers is larger than the mesh diameter of the screens, and aeration Tube (4), the membrane module box is provided with a filler replacement window (5), which is used for filler replacement and screen cleaning; the mesh diameter of the screen is 2mm; the granular filler used is round ceramsite with a density of 1.1kg /m ³ , the diameter is 2.5~3mm, the total volume of packing is 12.5% of the volume of the box between the bottom and the top screen; the flat membrane group used, the gap between each flat membrane is 25mm, when the air bubbles stir, the The gap ratio is not easy to cause blockage; the bottom aeration adopts high-pressure aeration, reduces the air intake volume and increases the intake pressure, and increases the circulation and stirring force of the aeration to the filler.

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